The major histocompatibility complex (MHC) is a set of linked genes which code for cell surface proteins involved in transplant rejection. The MHC contains three types of genes, class I, II and III (Klein J. et al.: Immunology: The Science of Self-Nonself Discrimination, pp. 687, 1984,John Wiley, Somerset, N.J.).
In humans, class I genes encode polymorphic 44,000 dalton glycoprotein chains that associate with a nonpolymorphic 12,000 dalton light chain, β2-microglobulin, and which are expressed on most cells of the body. Typical class I MHC genes are involved in regulating immune to viral infections (Zinkernagal R. M. et al. (1979) Adv. Immunol. 27:52–72).
In humans, the class II MHC antigens are cell surface glycoproteins composed of an α chain of approximately 35,000 daltons and a β chain of about 28,000 that are expressed only on subsets of immunologically active cells, such as β lymphocytes and macrophages.
Class III MHC genes code for serum proteins such as complement (C′).
The MHC loci in swine are known as the swine leukocyte antigens (SLA). In 1970, Vaiman et al., (Vaiman M. et al. (1970) Transplantation 10:155–161) and Viza et al. (Viza D. et al. (1970) Nature 227:949–951) provided descriptions of the SLA complex. These groups developed panels of SLA typing reagents (Vaiman M. et al. (1979) Immunogenetics 9:353–361) by preparing antisera of a defined specificity as well as by characterizing cells of known SLA type (homozygous typing cells) for use in mixed lymphocyte complex, to chromosome 7 (Geffrotin C. et al. (1984) Ann Genet (Parix) 27:213–219). The class I swine MHC loci are designated SLA-A,B,C. The class II swine MHC loci are designated SLA-DR, DQ. Because there are numerous genes coded by the SLA complex and because usually they are inherited as a unit, haplotype designations have been developed. For example, the SLAa haplotype codes for SLA-AaBaCaDRaDQa alleles.
Miniature swine are a good model for organ transplantation studies because of their breeding characteristics which make them one of few large animals in which genetics can be manipulated in a reasonable time, and also because of their size which permits surgical manipulations similar to those humans.